Spring frogs will be calling soon

By PETE EYHERALDE MCCB Naturalist
The Oskaloosa Herald

OSKALOOSA Tue, May 13 2008

— If you find yourself near a creek or pond this month, or maybe even just driving down the road, you’re likely to hear a new sound in the air. Not birds… or insects…, frogs! One of the sure signs of spring for many people is the year’s first frog calls. As the weather (and the water) warms up this month, frogs will be coming out of hibernation and starting to sing.
The first frog call you are likely to hear in Mahaska County is that of the western chorus frog. They’ll be calling from every small creek, flooded field and ditch around. And this year it looks like we’ll have a lot of flooded fields for them to choose from. The call of the chorus frog has been likened to the sound of a thumb running across the teeth of a fine toothed comb – sort of an ascending, vibrating whistle. This is a sound I’ve often been able to hear from the ditches, while driving down the road in my truck with the windows rolled up. In great numbers, at close distances the sound can be ear splitting. This big noise comes from a surprisingly little critter. Chorus frogs are usually gray-brown in color with three dark stripes down their back, but are no bigger than your thumb.
The second frog call of the year comes right on the heels of the chorus frog – sometimes within a couple of days or even on the same day. If you live near a wooded area with creeks or ponds you’re likely to hear the high pitched “peep-peep, peep-peep” of the spring peeper. This is also one of Iowa’s smallest frogs, about the size of the chorus frog, but with a dark “X” marking on the back. The spring peeper was once restricted to the forests of eastern Iowa, but in recent years it has been expanding its range westward.
Of course, all this spring singing is not just for fun. There’s serious business at work – breeding season. A few hardy, adventurous males locate an appropriate breeding pond when the temperature and humidity are suitable, and begin to call. Each species of frog has a distinct breeding call which entices females to join them and select a mate.
A male frog produces his call by a rapid back-and-forth movement of air over his vocal cords. When calling, a frog will close its mouth and nasal openings and force air from its lungs over the vocal cords into the mouth cavity, then back over the vocal cords and into the lungs. Producing a sound in this "closed system" enables some toads and frogs to vocalize under water. These animals use an enlarged throat or expandable vocal sac to resonate their calls.
Soon, other males congregate and add their voices to the chorus. Females, heavy with eggs, enter the pond, are grasped by a male in an embrace called amplexus, and begin the process of egg-laying and fertilization.
All of Iowa’s toads and frogs must return to a body of water to reproduce. Most of our anuran species breed during the spring or early summer. The majority of these amphibians select fishless bodies of water in which to breed. Flooded fields, ditches, small woodland ponds, prairie ponds and water-filled depressions are favorite places.
Frogs provide food for a wide variety of animals as well as people Their peeps, trills, whistles, grunts and snores add aesthetics to a spring evening. Learning to identify the species by the sounds they make can be an enjoyable spring pastime and as challenging as bird watching. See how many frog calls you can identify this month!

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